This invention relates to an electromagnetic-wave-operated heating apparatus in which high frequency energy is supplied to a three-dimensional resonator to produce an electric field thereby to heat a local portion of a body.
In a conventional electromagnetic-wave-operated heating apparatus, as shown in FIGS. 14 and 15, in the cavity 52 of a three-dimensional resonator 51 internal electrodes 53 are formed by depressing part of the cavity 52 or by using conductors to provide a concentrated electric field for heating (cf. Japanese Patent Application (OPI) No. 209073/1989 (the term "OPI" as used herein means an "unexamined published application")).
In the conventional apparatus, high frequency energy is applied to the three-dimensional resonator 51 to cause resonance in the cavity 52, which causes a strong electric field E to be formed between the internal electrodes and the conductor of the cavity 52 confronted therewith, while a strong magnetic field H is produced which surrounds the electric field E. The electric field E is enclosed by the strong magnetic field H so not to diffuse. A strong electric field is formed, concentrated at the central axis of the internal electrodes 53. With the electromagnetic field thus formed, a desired portion of a body 54 to be heated is heated with high concentration.
However, it has been found through experiments that, with the conventional electromagnetic-wave-operated heating apparatus, the results of heating are not always comparable to those which have been proposed.
As a result, the following facts have been found. When the body to be heated is in contact with the reentrants, the Q (quality factor) of the resonator is lowered, and the resonance frequency cannot be specified, so that it is impossible to heat the body. A gap between the body and the reentrants is needed. Only when the ends of the reentrants are parallel to each other, and the body to be heated is parallel to the ends of the reentrants can a deep local portion of the body be heated. However, in practice, these special conditions are rarely satisfied; the body to be heated is often not quite parallel or uneven. Thus, it is impossible to heat a local portion of the body with high concentration.